Chronic toxicity studies of Theophylline by the gavage route of administration using F344 rats and B6C3F1 mice will be conducted. The April 1987 General Statement of work will be followed. A brief description of these studies is as follows: A 104-week chronic toxicity study using three levels of Theophylline plus controls will be conducted. An interim evaluation at 65-weeks will include hematology. Additional mice shall be treated for blood level determinations. Blood samples shall be collected from both species at 1, 3, 6, 9, 15 and 24 months of the study. These samples will be processed frozen, and shipped to the NTP for the measurement of Theophylline levels.